Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy, is among the most common human genetic diseases and is the most common lethal genetic disorder of children. There is no cure for DMD and current treatment options serve only to slow somewhat progression of muscle wasting and loss of mobility while maintaining ventilation. Gene therapy represents a promising approach to treating or curing this recessively inherited disorder. However, numerous obstacles must be overcome before gene therapy can be applied routinely. These obstacles include a lack of knowledge of the safety and efficacy of dystrophin gene transfer to human muscle and an inability to target all the muscles of the body. Recently, a variety of mini-, micro- and full-length dystrophin cassettes have been shown to prevent the development of most or all dystrophic symptoms in mdx mice, a model for DMD. These cassettes can also be delivered efficiently to adult mdx mouse muscles using several viral vectors, including adeno-associated virus (AAV), resulting in a reversal of many dystrophic features. To explore the potential for gene therapy of DMD we propose to conduct a phase 1 human clinical trial of AAV-mediated gene transfer of a micro-dystrophin expression cassette. We propose to conduct extensive pre-clinical studies in the mdx mouse to explore the safety and efficacy of micro-dystrophin gene transfer using AAV serotype 6, which is enormously efficient at transducing skeletal muscle. The results of these studies will complement those of the other projects described in this Center application that are focused on dystrophic dogs and DMD patients. The combined results from these studies will be used to design, obtain regulatory approval for and implement a phase 1 clinical trial of AAV6-mediated micro-dystrophin gene transfer to DMD patients. Together, these studies will provide important new information on the potential for gene therapy for DMD.